1. Field of the Invention
This invention relates to methods for the manipulation of intercellular and intertissue interactions. The instant invention provides methods for the inhibition of cell adhesion to extracellular matrix components or the formation of functional basal lamina, and the manipulation of the results of such attachments. Thus the instant invention pertains to the modification of cellular interactions, with extracellular components, and methods for maintaining cell phenotype, developmental stage, and plasticity in vivo and in vitro.
2. Description of the Prior Art
The basement membrane (basal lamina) is a sheet-like extracellular matrix which is a basic component of all tissues. The basal lamina provides for the compartmentalization of tissues, and acts as a filter for substances traveling between tissue compartments. Typically, the basal lamina is found closely associated with an epithelium, or endothelium in all tissues of an animal including blood vessels and capillaries. The basal lamina components are secreted by cells, and then self assemble to form an intricate extracellular network. The formation of a biologically active basal lamina is important to the development and differentiation of the associated cells.
The Cnidarian, Hydra, is a simplified metazoan whose body wall is composed of an epithelial bilayer with an intervening extracellular matrix (ECM) termed the mesoglea. Hydra mesoglea have been shown to have a number of components seen in the ECM or basement membranes of higher invertebrates and vertebrates, these include: fibronectin, type IV collagen, laminin, and heparan sulfate proteoglycan. Hydra cell aggregation involves the complete morphogenesis of adult hydra from pellets of dissociated hydra cells. During this developmental process, cells segregate into an epithelial bilayer and then deposit a new extracellular matrix prior to the continuation of morphogenesis.
Extracellular matrix (ECM) components play a critical role in development through their affects on such cell processes as cell division, cell attachment, cell migration, and cell differentiation (reviewed by Timpl et al., 1989, Int. Rev. Exp. Pathol. 29:1-112; Damsky and Bernfield, 1991, Current Opn. in Cell Bio. 3:777-778; Hynes, 1992, Cell 69:11-25). It has been established that ECM/cell interactions are utilized by a wide range of vertebrate and invertebrate species to include such primitive organisms as the Cnidarian, Hydra. Hydra is particularly interesting in this regard because it represents one of the first animal phyla to develop defined tissue layers separated by an acellular extracellular matrix (Field et al., 1988, Science 239:748-752). Previous studies have shown that hydra ECM, termed mesoglea, contains type IV collagen, laminin, fibronectin, and heparan sulfate proteoglycans (Sarras et al., 1991a, Dev. Biol. 148:481-494). These molecules are continuously synthesized and deposited into the mesoglea in adult hydra and during hydra head regeneration (Hausman et al., 1971, J. Exp. Zool. 177:435-446). Other studies have shown that developmental processes in hydra such as head regeneration are dependent on the normal formation of ECM. These studies have shown that head regeneration in hydra morphogenesis can be blocked by using drugs that perturb collagen cross linking or drugs that interfere with proteoglycan GAG chain extension (Sarras et al., 1991b, Dev. Biol. 148:495-500). These studies have most recently been extended to the hydra cell aggregate system. This system allows one to form a pellet with dissociated hydra cells and then observe the complete regeneration of the adult hydra body within 72-96 hours through the process of cytodifferentiation and morphogenesis (Gierer et al., 1972, Nature New Biol. 239:98-101; Sarras et al., 1993, Dev. Biol. 157:383-398). Such studies of hydra development and the role of the ECM have focused heavily on a chemical approach (Barzanski et al., 1974, Amer. Zool. 14:575-581; Sarras et al., 1991ab, supra). Hydra cell aggregates first form an epithelial bilayer and then deposit an ECM before morphogenesis proceeds. Hydra cell aggregate development is blocked by drugs that perturb ECM formation and by antibodies raised against isolated hydra mesoglea. These studies demonstrate that functional studies of ECM/cell interaction can be carried out under in vivo conditions with hydra.
Type IV collagen has been shown to be a major structural component of basement membranes and has also been shown to be present in hydra ECM. The protomeric form of type IV collagen is formed as a heterotrimer made up from a number of different subunit chains called .alpha.1(IV), .alpha.2(IV) etc. The type IV collagen heterotrimer is characterized by three distinct structural domains: the non-collagenous (NC1) domain at the carboxyl terminus; the triple helical collagenous domain in the middle region; and the 7S collagenous domain at the amino terminus (FIG. 1) (Martin et al., 1988, Adv. Protein Chem. 39:1-50; Gunwar et al., 1991, J. Biol. Chem. 266:14088-14094). Type IV collagen exists as a supramolecular structure in ECM and this structure is thought to serve as a framework which provides mechanical stability to ECM (Timpl et al., 1986, supra) and as a scaffolding for the binding and alignment of other ECM molecules such as fibronectin, laminin, eutectin, and heparan sulfate proteoglycans (Gunwar et al., 1991, supra). The biological function of type IV collagen is critically related to the formation of an intact ECM since disruption of collagen cross linking by .beta.-aminopropionitrile interferes with the mesoglea formation and this leads to a blockage in normal hydra morphogenesis (Sarras et al., 1991b, 1993, supra).
Hydra cell aggregate development involves complete morphogenesis of adult hydra structures within 96 hr from pellets formed with dissociated hydra cells (Grierer et al., 1972, supra; Sato et al., 1992, Dev. Biol 151:111-116; Technau et al., 1992, Dev. Biol. 151: 117-127; Sarras et al., 1993, supra ). Morphologically, hydra cell aggregate development can be divided into two stages. The initial stage is from Time 0 to 24 hr when aggregates develop from a solid cell mass into a fluid-filled cyst where the outer wall is formed from an epithelial bilayer with an intervening ECM termed mesoglea. This stage involves active cell sorting between ectodermal and endodermal cells (Technau et al., 1992, supra) and subsequent mesoglea formation once the bilayer is established. The later developmental stages (24-96 hr) involve processes normally associated with tissue histogenesis; namely, alterations in the shape of epithelial layers, cell migration, cell differentiation, and other processes that result in morphogenesis of foot, head, and tentacle structures. In regard to the initial stages of hydra cell aggregate development, it has been shown that head regeneration in aggregates is not due to the clustering of cells from the original head regions. It has been suggested that head regeneration arises de novo (Gierer et al., 1972, supra ; Technau et al., 1992, supra ) from foci of developmental gradients established around the spherical aggregate. This indicates that cell differentiation or transdifferentiation into head region cells actively occurs during hydra cell aggregate development. In addition to positional information and possible activator influences, cells may differentiate or transdifferentiate under the influences of other developmental cues such as signals arising from the ECM.
Previous studies have shown that in vertebrates, fibronectin interacts with various collagens during matrix assembly, including type IV collagen (Carter, 1984, J. Cell Bio. 99:105-114). In addition, antibodies to the collagen binding domain of fibronectin had the ability to block ECM assembly by human lung fibroblasts. (McDonald, 1982, J. Cell Biol. 92:485-492). Other studies raised doubts as to the interaction, while polyclonal antibodies to the collagen binding domain blocked matrix assembly, purified collagen binding domains had no inhibitory effects in this assembly process (McDonald et al., 1987, J. Biol. Chem. 262:2957-2967; Hynes, 1990, Cell 48:549-554). In general fibronectin (FN) appears before collagen during assembly of vertebrate matrices, however, in the case of hydra ECM formation, FN and collagen appear in the mesoglea about the same time, based on immunofluorescent studies. Type IV collagen has been implicated as important in several human diseases (Hudson et al., 1993, J. Biol. Chem. 268:26033-26036). Basement membrane and its components have a role in lymphocyte adhesion, migration and proliferation (Li and Cheung, 1992, J. of Immunology 149:3174-3181).
The fundamental role ECM plays in tissue development and cell differentiation reverberates across phyla and kingdoms, to focus attention on the most basic elements that are required for all tissue interactions. The use of hydra as a model system for the study of basic elements of complex tissue interactions is a recognized approach. Instead of attempting to deduce the interaction between isolated tissues of higher order animals, the same mechanisms and phenomenon can be examined in vivo by using the complete animal, in hydra. This approach has led to the use of hydra to study the effects of glucose on tissue morphology, in an effort to understand the pathological effects of uncontrolled diabetes on kidney glomeruli, with excellent results (Zhang et al., 1990, Diabetologia 33:704-707).
Recently the .beta.1-laminin gene has been cloned and sequenced in hydra, showing very high homology with the human counter part. The homologues of fibronectin and collagen are present as well. It is a reflection on the fundamental role ECM plays, that hydra and higher order animals show the same cell matrix interactions, with similar components, domain interactions, receptor molecules and response to extracellular signals. Mammalian, and even human hormones, when applied to hydra result in bioactivity and effects on cell behavior. It is possible to use human insulin to stimulate cell proliferation in hydra. Other such cross-phyla activities can be attributed to many growth factors as well, i.e. EGF (epidermal growth factor), TGF-.beta., FGF (fibroblast growth factor), PDGF, to name a few.
Specific methods for the manipulation of cell adhesion to ECM, basal lamina, or adjacent cells would be useful for the in vivo manipulation of tissues and cells. Methods which address the fundamental elements of basic cell and tissue interactions are applicable to all systems which exhibit similar characteristic features. Such in vivo uses include, and are not limited to, inhibition of basal lamina formation, inhibition of basal lamina/cell interactions, and to encourage cells to maintain phenotypic plasticity. Such methods will also be useful for the in vitro manipulation of cells and tissues, for instance in maintaining cell cultures in undifferentiated or homeostatic states, non-enzymatic dispersal of cells from attachments, or the maintenance of confluent cells in suspension for propagation, maintenance, or collection.